FireFox 1.5

The most noticeable improvement in the user interface is the ability to reorder tabs via drag-and-drop. With Firefox 1.0, users had to view tabs in the order in which they were opened. Navigation is significantly faster, as Mozilla has implemented "intelligent caching" on the forward and back buttons, so the pages one is most likely to visit are preloaded—with no visible performance impact. User preferences have been redesigned to provide a cleaner tabbed interface, and features are more intuitively arranged.

But the most important Firefox tuneups are under the hood. Application and extension updates are now pushed to the background. This relieves the burden of having to upgrade the application and extensions manually, as with Firefox 1.0, and ensures that the latest security patches are applied.